This invention relates to improved methods and apparatus for securing together a plurality of strength members and, more particularly, relates to improved methods and apparatus for fastening together two wooden timbers or the like. In a specific embodiment of the present invention, an improved assembly of such timbers is provided which are especially suitable for use as a railroad tie or the like.
It is well known that wood is an especially suitable material insofar as structural purposes are concerned, not only because of obvious factors such as cost, ease of fabrication, strength and rigidity, etc., but also because of its relatively long useful life. In other words, the cellular character of wood does not render a wooden beam subject to failure because of fatigue, whereas the same unfortunately cannot be said for even the best of steels. Accordingly, wood is still very much preferred over other substances in the manufacture of many types of strength members wherein the penalty for sudden failure may be unacceptable.
For example, it is well known that most railroad ties are still made of wood, notwithstanding the present availability of many other apparently better materials and notwithstanding the fact that the cost of wood has increased to a substantial extent. Nevertheless, there are a great many miles of railroad in the United States and throughout the world, and although the average useful life of a wooden railroad tie is surprisingly good, it is nonetheless the case that a great many replacement ties are required each year. Accordingly, the cost of each railroad tie (including the tie-in-place, as well as the tie intended as a replacement) is a significant cost factor in the operation of any railroad systems.
It is well known, however, that most railroad systems in the United States employ heavier rolling stock than is commonly used throughout other portions of the world. This, in turn, increases the cost of tie installation and replacement in the United States, since more substantial trackage is a concomitant requirement of heavier rolling stock. Furthermore, the trend is to larger, and therefore even heavier, rolling stock in the United States. Accordingly, this tends to increase the demand for more substantial (i.e., stronger) ties.
It will be obvious that since wood is usually sold on a "board foot" basis, a larger railroad tie will necessarily cost more than a smaller tie. What is not well known, however, is that since a tie is conventionally fabricated as a single unit, an increase in tie size necessarily produces a resulting decrease in the number of trees (saw logs) which are large enough for such purposes, and this in turn produces an abnormal increase in the cost of fabricating a wooden railroad tie.
Although there is some variation in the size of ties used in trackage in the United States, most ties are 8-9 inches wide and 6-7 inches thick, depending on factors such as the intended use of the trackage and the special need of the particular railroad involved. For example, all ties must be 7 inches thick or greater unless the tie is to be used for a siding or the like, whereupon it may be only 6 inches thick. Whether an 8-inch wide tie is acceptable depends upon the weight which the tie may be expected to bear and upon the character of the road bed.
A tie which is expected to be used in a mainline track may be between 8 and 9 feet long, also depending on the character of the road bed. On the other hand, a tie which is to be installed at a switch may be 16 feet long or even longer.
All ties are treated with preservative, since the ties which are installed in sidings are as subject to deteriorations from insect attack and the like, as are ties in a mainline track. On the other hand, the ties in sidings are expected to have a much longer useful life since they are rarely subjected to an impact of the same magnitude as will be felt by a main track tie each time a train passes over at a high velocity. Accordingly, only a small number of the 6-inch thick ties are required each year, just as only a relatively small number of extra-long ties are required for switch installation or replacement. Instead, the great bulk of all wooden railroad ties which are now purchased or fabricated in the United States will be within the following schedule of dimensions: Width Thickness Length ______________________________________ 8" 7" 8', 81/2' or 9' 9" 7" 8', 81/2' or 9' ______________________________________
It will be readily apparent that only a relatively large and therefore more expensive saw log is suitable for fashioning a railroad tie of these dimensions. Accordingly, it will readily be apparent why there has long been a demand for a way to fashion an acceptable railroad tie out of two or more separate pieces of smaller size.
It is old, of course, to join two pieces of wood together for the purpose of providing a single piece of larger size. Accordingly, it is concededly old to glue, nail or otherwise fasten together two smaller wooden boards or beam to form a single large beam. Accordingly, many attempts have been made to form a less expensive railroad tie out of two or more smaller and therefore cheaper pieces of wood. The problem is that a railroad tie is subjected to a massive impact each time a piece of rolling stock passes over at a high enough speed. Furthermore, the impact tends to be delivered tangentially to the tie, which increases the likelihood that the tie will be split.
Attempts have been made to glue two tie-halves together to form a tie which will endure this shock. A railroad tie is conventionally treated with a preservative such as creosote, however, and this treatment tends to adversely affect the stability of the bond which is sought to be formed. Moreover, the two tie-halves are not identical insofar as grain and cell formation characteristics are concerned, and if one half tends to yield to the impact to a different extent, this also tends to break the bond between the two halves.
Nail-type joints are obviously less secure than conventional glue joints between two pieces of wood. Nevertheless, various complex techniques such as that described in U.S. Pat. No. 985,470 have been proposed from time to time which were intended to react in a compensatory way to the type of shock to which a railroad tie is subjected when a train passes over at a high speed. No such nail-type technique has ever been found to be satisfactory for such purposes. There has long been a demand for a commercially acceptable railroad tie which is formed out of two separate pieces, however, as is indicated by the many attempts to provide such a product. For example, see U.S. Pat. No. 197,721 which issued Dec. 4, 1877; U.S. Pat. No. 875,856 (Jan. 7, 1908); U.S. Pat. No. 985,470 (Feb. 28, 1911); U.S. Pat. No. 1,166,673 (Jan. 4, 1916); U.S. Pat. No. 1,436,573 (Nov. 21, 1922); and U.S. Pat. No. 2,701,399 (Feb. 8, 1955). Notwithstanding the fact that this long-existing demand has recently grown more acute, however, all of these prior art methods and apparatus have so far proved unsuccessful.